In the operation of a data processing system, e.g., a microprogrammed bank control and information system, it is often necessary to convert binary coded control signals and data signals from one code to another to transfer the information between data processing units which employ different code formats. Previous systems for achieving the necessary conversion between different code formats have required conversion circuits typically including numerous integrated circuit (IC) chips. Consequently, such circuits have been complex and expensive to fabricate.
The present invention is intended to provide an interface system for use between data processing units employing different code formats which is relatively uncomplicated in structure and inexpensive to manufacture in contrast to prior code conversion systems. An objective of the invention is to provide an emulation interface which advantageously utilizes read-only memory circuits to simplify the code conversion circuit and also permit looping programs to be implemented.